Chapter 11: The Auditory and Vestibular System Flashcards
Audition:
sense of hearing
Vestibular system:
sense of balance
Sound is audible variations of […].
Two types:
- […]
- […]
air pressure
compressed; rarefied
What determines pitch?
What determines loudness?
frequency
intensity
Frequency:
the number of compressed or rarefied patches of air that pass by our ears each second
We perceive high-frequency waves as having […] and high-intensity waves as having […].
higher pitch; louder
Sound wave movement within the ear:
- sound wave moves the tympanic membrane
- tympanic membrane moves the ossicles
- ossicles move the membrane at the oval window
- motion at the oval window moves fluid in the cochlea
- movement of fluid in the cochlea causes a response in sensory neurons
The generic sound neural response:
- signal is transferred to and processed by a series of nuclei in the brain stem
- output from these nuclei is sent to a relay in the thalamus, the medial geniculate nucleus (MGN)
- MGN projects to primary auditory cortex (A1) located in the temporal lobe
Why is the cochlea composed of water instead of air?
in order to resist movement which in turn will amplify the pressure
fluid has a greater inertia than air would
What is the attenuation reflex?
When is the response greater?
the onset of a loud sound triggers a neural response that causes muscles to contract
lower frequencies
What is the process that explains why we can hear voices in a noisy environment?
attenuation reflex
**it occurs while we speak
Perilymph:
fluid in the scala vestibuli and scala tympani
What is the ionic content like in the perilymph?
low K+ and high Na+
** similiar to CSF
Endolymph:
extracellular fluid in the scala media
What is the ionic content like in the endolymph?
high K+ and low Na+
Which fluid in the scala (component of the cochlea) has an unusual ionic content. Explain what this creates for audition?
active transport is done in the endolymph as both ions are against their concentration gradients
this enhances auditory transduction
What is the electrical potential of the endolymph?
+80 mV
What are the auditory receptors? Where are they located?
hair cells
Organ of Corti
Auditory receptors are called hair cells due to many […] extending from its top.
The critical event in transduction of sound into neural signal is […] of this cillia.
stereocilia
bending
Hair cells form synapses on neurons whose cell bodies are located in the […] within the […].
These axons of the […] enter the auditory nerve; a branch of the […].
spiral ganglion; modiolus
SG; auditory-vestibular nerve
SG cells are […].
bipolar
When the basilar membrane moves up…
Conversely, downward motion of the basilar membrane causes…
the reticular lamina moves up and in toward the modiolus
causes the reticular lamina to move down and away from the modiolus
Optimal orientation: As a microelectrode is advanced radially…
the preferred orientation remains the same for all the selective neurons from layer II down to layer VI
Orientation column:
radial columns of neurons that share the same microelectrode orientation selectivity
Optimal orientation: As a microelectrode is advanced tangentially…
the preferred orientation progressively shifts
Orientation-selective neurons are thought to be specialized for the…
analysis of object shape
What is direction selectivity?
Which receptive field (layer) exhibits direction selectivity?
fields respond when a bar of light at the optimal orientation moves perpendicular to the orientation in one direction but not in the opposite direction
many VI receptive fields
Direction-selective neurons are thought to be specialized for the…
analysis of object motion
Simple cells:
have distinct ON and OFF regions and are orientation selective
Complex cells:
do not have distinct ON and OFF regions instead give ON and OFF responses to stimuli throughout the receptive field
Simple and complex cells are typically [binocular/monocular] and sensitive to […].
binocular; stimulus orientation
What are the properties of neurons in the interblob areas (5)?
- binocularity
- orientation selectivity
- direction selectivity
- both simple/complex cells
- not wave length sensitive
What are the properties of most blob cells (3)?
Where do they receive input from?
The visual responses of blob cells most resemble what?
- wavelength sensitive
- monocular
- lack orientation selectivity and direction selectivity
- directly from the koniocellular layers of the LGN
- magnocellular and parvocellular input via layer IVC
resemble those of the koniocellular and parvocellular input
What is the receptive field shape of most blob neurons?
circular
Blob channels appear to be specialized for the […].
analysis of object color
**receptive field of red-green blue-yellow color opponency in the center of their receptive field or double opponent cells (color-opponent center and color-opponent surround) etc.
Without blob channels, we might be…
colorblind
List the parallel pathways:
- magnocellular pathway
- parvo-interblob pathway
- blob pathway
Describe the magnocellular pathway:
Retina = M-type ganglion cells
LGN = Magnocellular
V1 = Layer IVC (alpha) — IVB
Extrastriate cortical areas
**Layer IVC can also go to blob and then towards extrastriate cortical areas
Describe the Blob pathway:
Retina = nonM-nonP ganglion cells
LGN = Koniocellular
V1 = Blob
Extrastriate cortical areas
** In Layer V1, Blob cells can receive input from Layer IVC (M/P path)
Describe the Parvo-interblob pathway:
Retina = P-type ganglion cells
LGN = Parvocellular
V1 = Layer IVC (beta) — Interblob regions (Layer II/III)
Extrastriate cortical areas
**Layer IVC can also go to blob and then towards extrastriate cortical areas
Name the “best guess” of the function of each parallel pathway:
Magnocellular pathway is motion
Blob pathway is color
Parvo-interblob pathway is shape
Why is the magnocellular pathway thought to be involved in the analysis of object motion and the guidance of motor actions?
- large receptive fields
- highest percentage of direction-selective neurons
- contains neurons with transient responses
Why is the parvo-interblob pathway suggested to be involved in the analysis of fine object shape?
- neurons in this pathway have the smallest orientation-selective receptive fields
Typical receptive fields in the blobs are […] surround and […]. They are often [binocular/monocular] and lack […].
center-surround and color opponent; monocular; orientation selectivity
Why is the blob pathway suggested to be involved in the analysis of object color?
- high incidence of wavelength sensitivity
What is contained in a 2 x 2 mm chunk of cortex (3)?
- two complete sets of ocular dominance columns
- 16 blobs
- (in between blobs) all 180 degree of possible oreintations
Cortical module:
a unit of brain tissue from the visual cortex that is both necessary and sufficient to analyze the image of a point in space
Striate cortex is called…
V1 for visual area one
Why is the striate cortex called V1?
it is the first cortical area to receive info from the LGN
What does the cortical dorsal stream serve for visual processing?
analysis of visual motion and the visual control of action
What does the cortical ventral stream serve for visual processing?
perception of the visual world and the recognition of objects
Dorsal stream neurons are most similar to […]. in V1, and ventral stream neurons are most similar to […] in V1.
magnocellular; combining features of parvo-interblob and blob cells
-20 nm displacement of cillia vs 20 nm:
-20 = hyperpolarization 20 = depolarization
What channel is on the tips of the stereocilia?
What is each linked to the wall of the adjacent cilium?
TRPA1
tip link
When the cilia are straight, occur the resulting tip link and ion movement:
T: tension that holds channels partially opened
I: K+ leakage from endolymph to hair cell
When the cilia is displaced in opposite directions, results in the tip link and ion movement responses:
ONE WAY
T: tension increase
I: K+ inward current
OPPOSITE
T: tension decrease; close K+ channels
I: cease K+ current
The entry of K+ into the hair cell causes what list of events…
- depolarization
- activates voltage gated Ca2+ and influx
- NT glutamate release
- activates the spiral ganglion fibers postsynaptic to the hair cell
Outer hair cells respond to sound with both…
- receptor potential; change in voltage
2. change in length (motor proteins)
Motor proteins is also known as […].
Bending of the stereocilia causes […] to enter the hair cell, […] it and triggering motor proteins to […] the hair cell.
The shortening/lengthening of the hair cell increases…
prestin
K+; depolarizing; shorten
the flexing of the basilar membrane
Besides motor proteins, how else can the outer hair cells be modified?
the cochlea receives efferent input by releasing acetylcholine
Without the outer hair cells amplification effect what can occur (damage to outer hair cells)?
When prestin is eliminated, what occurs?
lead to deafness
near deafness
All ascending auditory pathways converge onto the […].
inferior colliculus
List the auditory pathway starting from the cochlea to MGN:
cochlea — spiral ganglion — auditory nerve fiber — V/D cochlear nucleus — V: superior olive (both sides) — inferior colliculus [lateral lemniscus] —MGN — auditory cortex
Axons innervate the dorsal cochlear nucleus and ventral cochlear nucleus […] to the cochlea where the axons originated.
ipsilateral
Projections of the inferior colliculus send axons to the MGN and also …
superior colliculus
Superior colliculus:
integration of auditory and visual information
Which nuclei receives input from just one ear, from both?
What does this mean when someone is deaf completely in one ear only?
ONE
- dorsal
- ventral
BOTH
- all other nuclei
complete deafness is only if a cochlear nucleus (auditory nerve) is destroyer on one side
Characteristic frequency:
neuron is most responsive to sound at one frequency
Describe the frequency characteristic value down the apex
moving from base to apex, a progressive decrease in the frequency that produces the maximal deformation of the membrane
Stimulus intensity:
firing rates or neurons and the number of active neurons
As a stimulus gets more intense, the basilar membrane […], causing the membrane potential of the activated hair cells to be more […].
greater amplitude; depolarized/hyperpolarized
Tonotopy:
systematic organization of characteristic frequency within an auditory structure
TONOTOPY: At a fixed frequency, how could you produce membrane deformation at a point farther up the nasilar membrane?
more intensity
Phase locking:
consistent firing of a cell at the same phase of a sound wave
Phase locking can only be used for
sound waves up to about 4 kHz (above is too fast)
Tonotopy can be used for
frequencies are represented by tonotopy alone
What encoding techniques are used for the following situations:
very low frequency: phase locking
intermediate: both
high frequency: tonotopy
Interaural time delay:
angles that sound approaches you that reach one ear faster than the other
When can ITD not be used?
high frequencies
Interaural intensity difference:
sound localization at high frequencies; sound shadows
Duplex theory of sound:
- ITD
2. IID
20-2000 Hz uses […] while 2000-20000 Hz uses […].
ITD; IID
How can binaural neurons (starting with the superior olive) contribute to sound localization?
delay lines only at low frequencies
inhibition
interaural intensity
**sound triggers AP in LE first ex. takes a few ms after to reach other ear
How can vertical localization of sound be impaired?
outer ear curvature; pinna
Otolith organs
detect the force of gravity and tilts of the head
Semicircular canals
sensitive to head rotation; angular acceleration
Otolith organs consists of
saccule and utricle
large and at the center
Vestibular nerve axon cell bodies lie in […] ganglion
scarpas
Saccule and utricle detect changes of […] as well as
head angle ; linear acceleration
Otolith organs kinocilia response vs Semicircular canals:
O: inhibit and excite some
S: inhibit/excite all in one and opposite in the other (counterrotation)
